The present invention relates to a method of bend-shaping a glass plate in a heating furnace and an apparatus for bend-shaping the glass plate. More particularly, the present invention relates to an improved method of and apparatus for bend-shaping the glass plate suitably used for deeply bending a side portion of the glass plate.
Generally, a laminated glass is formed by laminating two glass plates and an intermediate plastic film such as polyvinyl butyral as an interlayer, and it is widely used particularly for a windshield for an automobile from the standpoint of safety.
In such laminated glass of this kind, it is necessary to bend two flat glass plates to thereby form a laminated glass because there is a demand for the laminated glass having a curved surface from the viewpoint of excellent design for automobiles. In this case, when the glass plates are separately bent, a subtle difference in the shape of curve appears between the glass plates to be laminated. Accordingly, when they are laminated with the intermediate layer interposed therebetween, there results disadvantages such as that a complete joint between the two glass plates and the interlayer is not obtainable, or air bubbles are left at the surfaces of bonding when manufactured or in use, this causing the peeling-off of the laminated glass. Accordingly, a method of bending simultaneously two overlapping glass plates has been used for manufacturing the laminated glass.
As a conventional method of bend-shaping glass plates for a laminated glass, there has been known such a method that a bending mold having a bend-shaping surface corresponding to a curved surface of the laminated glass is prepared; two glass plates are placed on the bending mold in an overlapping state; the bending mold is transferred into a heating furnace together with the glass plates; the glass plates are heated to a temperature capable of softening glass so that the glass plates are bent by their own deadweight as the glass plates are softened, whereby the glass plates are bent so as to correspond to the bend-shaping surface of the bending mold (Japanese Examined Patent Publication No. 10332/1974).
In such method, when it is necessary to bend deeply a side portion of the laminated glass, there is used a bending mold having a fixed split mold portion in a ring form which has a bend-shaping surface corresponding to an intermediate curved portion of the laminated glass and a movable split mold portion in a ring form which is placed at a side (or both sides) of the fixed split mold portion so that it can move to the fixed mold portion so as to be in alignment with the fixed mold portion by its own deadweight, and which has a bend-shaping surface corresponding to a portion to be deeply bent of a side portion of the laminated glass. Two glass plates in a flat form are placed in an overlapping state on the bending mold with the movable split mold portion (portions) so that the movable split mold portion is developed; the bending mold is transferred into a heating furnace along with the glass plates; the glass plates are heated; and as the glass plates are softened, the movable split mold portion is moved so as to come into alignment with the fixed mold portion, whereby the side portion of the glass plates is deeply bent by their deadweight by means of the movable split mold portion.
In the conventional method of bend-shaping the glass plates for a laminated glass and when the both side portions of the overlapping glass plates are to be deeply bent, the side portions of the overlapping glass plates are forcibly bent-shaped by means of the movable split mold portions which are moved by the own deadweight of the glass plates. However, when the side portions of the overlapping glass plates are to be further deeply bent, the following disadvantage results. Namely, although the peripheral portion of the deeply bent portions of the glass plates can follow the shape of the bend-shaping surfaces of the movable split mold portions, the softened glass plates can not follow a desired radius of curvature of the curved surface excluding the peripheral portion of the deeply bent portions of the overlapping glass plates. Accordingly, the shaping operation for the deeply bent portions of the overlapping glass plates is insufficient. There is an attempt to heat locally the portions to be deeply bent of the glass plates to thereby make the bending operation easy. However, such method is still insufficient.
In order to solve the above-mentioned problem, it is considered to use a pressing method wherein the glass plates are interposed between a convex mold and a concave mold so that a correct curved shape of the glass plates is obtainable. In this method, however, the overlapping glass plates have to be simultaneously bend-shaped. Accordingly, it is necessary to correctly place the two overlapping glass plates and to hold them at the time of bend-shaping. However, when the two overlapping glass plates are to be held by using known techniques such as a hanging method or a sucking method, it is still insufficient to correctly position the overlapping glass plates, and as a result, the above-mentioned pressing method can not be used.
FIG. 13 shows an example of a split type bending mold 110 adapted to bend-shape two overlapping glass plates by utilizing the deadweight of the glass plates. The bending mold 110 is mounted on a base truck 126 which constitutes a transferring means. The bending mold 110 comprises a ring-like fixed split mold portion 111 having a bend-shaping surface 111a corresponding to the intermediate curved portion excluding both side portions of the overlapping glass plates 101 which are to be subjected to a deeply bending operation, and ring-like movable split mold portions 112 each having a bend-shaping surface 112a corresponding to a portion to be deeply bent of the glass plates 101 which are to be formed into a laminated glass plate 101, the bend-shaping surface 112a coming in alignment with the bend-shaping surface 111a of the fixed split mold portion 111 when the movable split mold portions 112 are moved to a set position at both sides of the fixed split mold portion 111. The fixed split mold portion 111 is fixed onto the base truck 126 by means of supporting bars 113, and both side portions in the width direction of each of the movable split mold portions 112 are respectively supported at the free ends of the supporting bars 115 provided on fixed brackets 114 of the base truck 126 so as to be swingable. Further, a balance weight 117 is attached to the supporting portion of each of the movable split mold portions 112 by means of a moment arm so as to be moved to the set position whereby the movable split mold portions 112 are in alignment with the fixed split mold portion 111.
FIG. 13a shows the bending mold on which two flat glass plates are placed in an overlapping state before they are subjected to the heating operation. FIG. 13b shows that the bending operation for the glass plates has been finished. FIG. 13c is a plan view for illustrating a state that the bending mold is split. The bending mold assumes a position that the movable split mold portions are in alignment with the fixed split mold portion before the flat glass plates are placed on the bending mold. However, when the flat glass plates are placed on the bending mold, the movable split mold portions are automatically split due to the deadweight of the glass plates, whereby the bending mold assumes the state as shown in FIG. 13a. The construction of the movable split mold portions may be changed in design as desired so long as they can move in the direction capable of aligning with the fixed split mold portion due to the deadweight of the glass plates and to stop at the position in alignment with the fixed split mold portion. The direction of the movable split mold portions to the original set position can be adjusted by using some structural elements of the movable split mold portions or weights.
In case of press-shaping the glass plates on the split type bending mold by using an auxiliary pressing member so as to deeply bend portions of the glass plates from the upper direction, there sometimes takes place a phenomenon that a portion of the movable split mold portions which is close to the fixed split mold portion jumps up, this causing the deformation of a local portion of the glass plates. FIG. 3 is a diagram showing the above-mentioned phenomenon.
In FIG. 3, a reference numeral 1 designates a working surface of pressing load, a numeral 2 designates the bending mold and a numeral 3 designates a pivotal shaft for a movable split mold portion. In such typical bending mold, a moment of force resulting around the pivotal shaft applied to the movable split mold portion due to a pressing load functions to separate the bend-shaping surface of the movable split mold portion away from the bend-shaping surface of the fixed split mold portion, whereby there results the jumping phenomenon as described above.
In order to solve the above-mentioned problem, the following method has been proposed. Namely, the glass plates are bent by their deadweight on a so-called split type bending mold comprising movable split mold portions and a fixed split mold portion; side portions of the glass plates which are to be deeply bent are pressed by auxiliary pressing members from the upper direction of the glass plates while the movable split mold portions are clamped with respect to the fixed split mold portion, whereby the deeply bent portions are provided. The clamping operation is conducted to prevent the movable split mold portions from opening when the pressing operation is carried out. In order to assure a sufficient clamping function, it is necessary to support the movable split mold portions by raising them at the outside of the each of the pivotal shafts with respect to the fixed split mold portion, and to exert a force so that the bend-shaping surface of the movable split mold portions comes in alignment with the bend-shaping surface of the fixed mold portion inwardly from each of pivotal shafts with respect to the bend-shaping surface of each of the movable split mold portions.
FIG. 2 is a side view showing an example of the bending mold having the above-mentioned clamping structure, wherein a reference numeral 4 designates a weight clamping jig, a numeral 5 designates a pushing rod clamping jig, a numeral 6 designates a pushing rod, a numeral 10 designates a hinge, a numeral 13 designates an auxiliary pressing member, a numeral 1115 designates a weight, a numeral 16 designates a bending mold and a numeral 17 designates a glass.
However, the above-mentioned supporting structure using pushing means has difficulty in the adjustment of the height of the pushing rod 6 for each bending mold because the pushing operation has to be carried out from the outside of the heating furnace in order to avoid the disadvantage that a driving section is exposed in the high temperature of the heating furnace, and there often results local deformation at the portion of the laminated glass plate corresponding to the border portions between the movable split mold portions and the fixed split mold portion.